The advancement of enhanced materials for the use of medical implants, such as joint prostheses, has immensely improved the quality of life for many people over the past century. Devices such as artificial hips, knees, shoulders and other devices have allowed people who would otherwise have suffered from chronic pain and physical limitation to live active, comfortable lives. The development of such devices has confronted scientists and engineers with many technical challenges, such as in the area of materials science engineering, where various biocompatible materials with different physical and mechanical properties are bonded to each other in order to achieve optimal implant performance.
However, over the past several decades, surgical implants have been manufactured by making a near-net-shape part by forging or casting followed by machining and finishing operations for the desired surface. These operations require expensive tooling and only make sense for large volume production. Using similar practice, manufacturing of patient matched or low volume implants become a cost intensive effort and are rarely practiced. Other challenges such as difficulty in machining of titanium alloys due to high strength, low ductile yield make it even more expensive to machine titanium (Ti) based implants commercially. In addition, conventional manufacturing technologies are energy intensive, produce significant amounts of materials waste and cannot produce devices with functional gradation.
Additive manufacturing (AM) represents a new option for production of orthopedic implants. Although AM requires final machining or hand finishing, it allows significant flexibility towards manufacturing low-volume, complex implants. U.S. Pat. No. 7,666,522 to Justin et al., issued on Feb. 23, 2010, and which is incorporated herein by reference, discloses a method for purportedly depositing a hard wear resistant surface onto a porous or non-porous base material of a medical implant. The wear resistant surface of the medical implant device in Justin et al. may be formed by a Laser Based Metal Deposition (LBMD) method such as Laser Engineered Net Shaping (LENS).
Materials used for such devices must not only be non-corrosive, but must also be sufficiently resilient (having high tensile and compressive strength), and hard (having sufficient wear resistance). Since a device such as an artificial joint must undergo a great number of cycles of wear during the lifetime of the host patient, such devices must also possess great fatigue properties.
Justin et al. purportedly addresses the need for a device, such as an artificial joint, which can take advantage of the properties of a first material, such as the porosity of porous tantalum (Ta) or Ti, and also take advantage of the properties of a second material, such as the hardness of a material like alloys of cobalt and chrome (Co—Cr), for use in a bearing environment such as a ball or socket of a joint. According to Justin et al., such a device would preferably not exhibit any delamination between the two materials and would not experience any galvanic corrosion. In addition, Justin et al. discloses that such a device would also preferably not diminish the porosity of the porous material due to the flow of the other material thereinto.
Typically for load-bearing biomedical devices, Co and Cr materials are used for construction of most devices, in particular the CoCrMo alloy. However, concerns related to higher amounts of Co and Cr ion release in recent years prompted the U.S. Food and Drug Administration in 2010 to direct leading implant manufacturers to conduct post-market studies of their devices to determine whether a high level of metallic debris was being released into a patient's body.
Though metal-on-metal devices may offer greater motion, higher stability and greater than 99% reduction in wear debris compared to ultra high molecular weight polyethylene (UHMWPE) components in lab experiments, concerns are growing related to excess metallic ions being released in the body that can cause metallosis, severe tissue and bone damage. Accordingly, there is a need to address the problems in the prior art.